Fail safe throttle positioning system

ABSTRACT

A fail-safe throttle positioning device is disclosed for an engine induction system. A throttle body is provided having a fluid passage. A movable throttle valve is disposed within the fluid passage for at least idle speed control. An actuator mechanism is connected to the throttle valve for operably moving the throttle valve between a minimum fluid flow position and a maximum fluid flow position. A fail-safe mechanism urges the throttle valve toward an intermediate position between the minimum and maximum fluid flow positions to prevent inoperability of the engine during failure of the actuator mechanism.

FIELD OF THE INVENTION

The present invention relates to an air metering throttle body assemblyfor an internal combustion engine, and more particularly, to a throttlepositioning device to prevent inoperability of the engine during failureof the throttle actuator.

BACKGROUND OF THE INVENTION

A typical throttle body assembly in present-day use takes the form of aone-piece metal casting formed with a main bore or flow passageextending through the body along a first axis which is intersected by athrottle shaft bore extending through the body along a second axisperpendicular and intersecting the axis of the main bore. A circularthrottle plate is mounted within the main bore on a shaft rotatablysupported in the shaft bore. By rotating the shaft, the plate can bemoved between a blocking or minimum flow position, in which the plate isgenerally perpendicular to the axis of the main bore, to a maximum openposition in which the plate is aligned with the bore axis to therebymeter flow through the main bore.

Throttle control valve systems have recently been developed whichoverride the driver's command as represented by his positioning of theaccelerator pedal by taking over control of the throttle. These systemsare frequently referred to as “electronic throttle control” or “drive-bywire” systems in that there is no direct mechanical connection betweenthe accelerator pedal and the throttle, the pedal position beingtransmitted to an electronic control unit as an electric signal which isprocessed by the control unit and transmitted by the control unit in theform of an electric signal to an electromechanical throttle actuator.This type of “drive-by wire” system may also be adapted for sensing thespeed of the engine driven wheels with respect to that of the non-drivenwheels, so that if the speed of the driven wheels becomes greater thanthat of the non-driven wheels, the control unit can transmit an electricsignal to the electromechanical actuator which alters the position ofthe throttle plate to reduce the torque output of the engine until theengine driven wheels regain traction.

While such “drive-by wire” systems, in general, are quite reliable, amalfunction of the electrical supply system or the electronic controlunit can result in a total loss of control by the driver over thethrottle valve position in that the sole control over the position ofthe throttle valve is an electrical signal from the electronic controlunit, and there is no direct mechanical connection between theaccelerator pedal and the throttle valve. In the worst case, anelectrical or electronic malfunction could result in unintended anduncontrollable acceleration of the vehicle, should the throttle plate,upon the loss of its electrical positioning signal, be in or moved to awide open position. Consequently, most throttle plates are spring-biasedto move to a closed position in response to loss of an electricalcontrol signal, rendering the vehicle more or less effectivelyimmobilized in that the idle air flow will be reduced to a minimum.

SUMMARY OF THE INVENTION

The present invention is directed to providing a fail-safe throttlepositioning system to prevent inoperability of the engine during failureof the throttle actuator and to maintain the ability to continue todrive at a limited, but reasonable speed in the event of suchmalfunction by placing the throttle valve in a “limp home” mode wherethe throttle valve is positioned intermediate between the minimum andmaximum flow positions. The actuator mechanism can include a throttlelevel connected for rotation to a shaft supporting the throttle valve.The throttle lever may include a first surface engageable with a firststop defining a minimum fluid flow position and a second surfaceengageable with a second stop defining a maximum fluid flow position.Throttle spring means urges the throttle lever toward the normal minimumfluid flow position. The fail-safe mechanism may include a fail-safelever rotatably mounted on the shaft supporting the throttle valve. Thefail-safe lever may include a first surface engageable with the throttlelever and a second surface engageable with a fail-safe stop. Fail-safespring means urges the fail-safe lever toward the fail-safe stop so thatthe throttle lever is held in the intermediate position until driven bythe actuator mechanism toward one of the minimum and maximum fluid flowpositions. The actuator means may also include a mechanically operatedactuator means connected to the throttle lever at one end and to thedriver actuated accelerator mechanism, such as a pedal, at the other endto be responsive to driver input. The mechanically operated actuatormeans may include a cable connected between the throttle lever and theaccelerator mechanism actuated by the driver. In the alternative, theactuator means may include an electrically operated actuator meansconnected to the throttle lever at one end and connected to theaccelerator mechanism at the other end to receive driver input. Theelectrically operated actuator means may include what is typicallyreferred to as “electronic throttle control” or “drive-by wire”configuration.

Other objects, advantages and applications of the present invention willbecome apparent to those skilled in the art when the followingdescription of the best mode contemplated for practicing the inventionis read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The description herein makes reference to the accompanying drawingswherein like reference numerals refer to like parts throughout theseveral views, and wherein:

FIG. 1 is a plan view of a full-safe throttle position device for anengine induction system mounted on a throttle body according to thepresent invention;

FIG. 2 is a side elevational view of the fail-safe throttle positioningdevice as illustrated in FIG. 1;

FIG. 3 is a detailed cross-sectional view of the fail-safe throttlepositioning device as illustrated in FIG. 1 with certain portionsremoved and other portions shown in cross-section;

FIG. 4 is a schematic view of a throttle valve within a fluid passage ofa throttle body for movement between predefined positions according tothe present invention; and

FIG. 5 is a simplified exploded perspective view of a shaft, a throttlevalve lever and a fail-safe lever according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The fail-safe throttle positioning system 10 can be part of aconventional mechanically operated engine induction throttling device,such as a throttle body 12, with a direct acting idle speed control,such as a movable throttle valve 14, for use with a spark ignitionengine. The fail-safe throttle positioning system 10 of the presentinvention can also be incorporated into an electric operated engineinduction system throttling device that provides complete drive-by wirefunctions of idle speed control, traction control, transmission shiftharshness control, vehicle speed control and deceleration air control ona spark ignition engine. In its simplest form, the fail-safe throttlepositioning device 10 according to the present invention includes thethrottle body 12 with a movable throttle valve 14 for at least idlespeed control mounted for movement with respect to the throttle body 12.The movable throttle valve 14 is disposed in a fluid passage 16 formedin the throttle body 12 for controlling fluid flow through the fluidpassage 16 in response to movement of the throttle valve 14. Actuatormeans 18 is connected to the throttle valve 14 for operably moving thethrottle valve 14 between a minimum fluid flow position 20 and a maximumfluid flow position 22. Fail-safe means 24 urges the throttle valve 14toward an intermediate fluid flow position 26 between the minimum andmaximum fluid flow positions, 20 and 22 respectively, to preventinoperability of the engine during failure of the actuator means 18.

The actuator means 18 may include a throttle lever 28 connected to ashaft 30 supporting the throttle valve 14 within the fluid passage 16 ofthe throttle body 12. The throttle lever 28, shaft 30 and throttle valve14 moving in rotation with one another. The throttle lever 28 includes afirst surface 32 engageable with a first stop 34 defining the minimumfluid flow position 20. A second surface 36 of the throttle lever 28engages with a second stop 38 defining the maximum fluid flow position22. Throttle spring means 40 normally urges the throttle lever 28 towardthe minimum fluid flow position 20. The actuator means 18 may alsoinclude a mechanically operated actuator means connected to the throttlelever 28 and responsive to driver input, or alternatively may include anelectrically operated actuator means connected to the throttle lever 28and responsive to driver input. The electrically operated actuator meansmay include a “drive-by wire” configuration where the throttle lever 28is operably actuated by a reversible electric motor 42 having a radiallyextending drive arm 44 supporting a drive pin 46 drivingly engagedwithin an elongated slot 48 formed in the throttle lever 28. Theradially extending drive arm 44 and connected drive pin 46 are driven inrotation about the shaft of the reversible electric motor 42 in responseto electric signals for driving the reversible electric motor in thedesired direction to position the movable throttle valve 14 in thedesired fluid flow position.

The fail-safe means 24 may include a fail-safe lever 50 rotatablymounted with respect to the shaft 30 so that the fail-safe lever 50 canrotate independently of the shaft 30. The fail-safe lever 50 includes afirst surface 52 engageable with the throttle lever 28, such as withlongitudinally extending throttle tab 54. A second surface 56 of thefail-safe lever 50 engages with a fail-safe stop 58. Fail-safe springmeans 60 urges the fail-safe lever 50 toward the fail-safe stop 58 sothat the throttle lever 28 is driven through contact between thefail-safe lever 50 and the longitudinally extending throttle tab 54formed on the throttle lever 28 until it reaches the intermediate fluidflow position 26 corresponding to the fail-safe lever 50 engaging thefail-safe stop 58. The throttle lever 28 is held in the intermediateposition 26 until driven by the actuator means 18 toward one of theminimum and maximum fluid flow positions, 20 and 22 respectively.

The fail-safe means 24, in the preferred embodiment as illustrated inFIG. 3, may also include a spacer sleeve 62 mounted on the shaft 30external of the throttle body 12. The external portion of the shaft 30may include a non-circular section as best seen in FIG. 2 for engagementwith the throttle lever 28. The spacer sleeve 62 may include a reduceddiameter, longitudinally elongated surface 64 and adjacent one end anenlarged diameter annular shoulder 66. The fail-safe lever 50 isengageable rotatably on the enlarged diameter, annular shoulder 66 ofthe spacer sleeve 62, allowing the fail-safe lever 50 to rotateindependently of the shaft 30. The fail-safe spring means 60 may includea helical spring 68 extending longitudinally over the reduced diameter,longitudinally elongated surface 64 of the spacer sleeve 62. A first end70 of the helical spring 68 is connected to the throttle body 12 and asecond end 72 of the helical spring 68 is connected to the fail-safelever 50 for normally urging the fail-safe lever 50 toward engagement ofthe second surface 56 of the fail-safe lever 50 with the fail-safe stop58 to thereby hold the throttle lever 28 in the intermediate fluid flowposition 26. Spring bushings, 74 and 76, are disposed at thelongitudinal ends of the helical fail-safe spring 68 and overlaylongitudinally at least a portion of the fail-safe helical spring 68.The spring bushings, 74 and 76, include an external surface 78 extendinglongitudinally. The throttle spring means 40 can include a helicalthrottle spring 80 extending longitudinally over the spring bushings, 74and 76. The helical throttle spring 80 has a first end 82 connected tothe throttle body 12 and a second end 84 connected to the throttle lever28 to normally urge the throttle lever 28 toward the minimum fluid flowposition 20 where the first surface 32 on the throttle lever 28 engagesthe first stop 34. The throttle spring means 40 has less force than thefail-safe spring means 60, so that the fail-safe spring means 60 is ableto drive the throttle lever 28 to the intermediate fluid flow position26 through fail-safe lever 50 contacting the longitudinally extendingthrottle tab 54 of the throttle lever 28 with the first surface 52 ofthe fail-safe lever 50. The fail-safe lever 50 is urged by the fail-safespring means 60 toward the intermediate fluid flow position 26 where thesecond surface 56 of the fail surface lever 50 engages the fail-safestop 58.

The fail-safe throttle positioning system 10 according to the presentinvention for a mechanically operated throttle device with direct actingidle speed control device can include a throttle lever 28 for directconnection to the throttle shaft 30 and throttle valve 14, along withprovisions for attachment to the vehicle throttle system. A fail-safeposition lever 50 contacts a fixed stop 58 and the idle speed controllever 28 or throttle lever 28. The fail-safe lever 50 is held in placeagainst the fixed fail-safe stop 58 by a fail-safe spring means 60. Theidle speed control lever or throttle lever 28 provides an attachmentpoint for an idle speed actuator means 18. A throttle return springmeans 40 provides normal throttle system return force and is attachedthe throttle body 12 at one end and the throttle lever 28 at the otherend. The throttle return spring means 40 has less force than thefail-safe spring means 60. The system allows the idle speed controlactuator means 18 to position the throttle valve anywhere in the rangefrom minimum idle air flow throttle valve set position, such as minimumfluid flow position 20 to some predetermined throttle valve positionthat allows more air flow than the fail-safe position, such as maximumfluid flow position 22. In the event that the idle speed controlactuator means 18 loses force, the fail-safe throttle positioning system10 is intended to provide a predetermined throttle valve positiongreater than the minimum idle air flow set position, such asintermediate fluid flow position 26. The fail-safe throttle positioningsystem 10 functions properly only if the vehicle throttle system is freeto move over its entire operating range.

The fail-safe throttle operating system 10 for an electrically operatedthrottling device can include a throttle control lever 28 contacting thefail-safe position lever 50. The throttle control lever 28 provides anattachment point for the throttle control actuator means 18. Thefail-safe position lever 50 contacts a fixed fail-safe stop 58 and thethrottle control lever 28. The fail-safe lever 50 is held in placeagainst the fixed fail-safe stop 58 by fail-safe spring means 60.Throttle spring means 40 provides normal throttle system return forceand is attached to the throttle body 12 at one end and the throttlecontrol lever 28 at the other end. The throttle return spring means 40has less force than the fail-safe position spring means 60. Thefail-safe throttle positioning system 10 according to the presentinvention allows the throttle control actuator means 18 to position thethrottle valve 14 anywhere in the range from minimum idle air flowthrottle valve set position, such as minimum fluid flow position 20, toa wide open throttle position, such as maximum fluid flow position 22.In the event that the throttle control actuator means 18 loses force,the fail-safe throttle positioning system 10 is intended to provide apredetermined throttle valve position greater than the minimum idle airflow set position, such as intermediate fluid flow position 26.

In operation, when the actuator means 18 is in a de-energized state, orfailure mode, the throttle spring 80 urges the throttle lever 28 in aclockwise direction as illustrated in FIG. 2 toward engagement of thefirst surface 32 of the throttle lever 28 with the first stop 34. Beforereaching the minimum fluid flow position 20 where the first surface 32engages the first stop 34, the clockwise rotational urging of thethrottle spring 80 is overcome by the counterclockwise urging of thefail-safe helical spring 68 to maintain the second surface 56 of thefail-safe lever 50 against the fail-safe stop 58 through contact of thefirst surface 52 of the fail-safe lever 50 with the longitudinallyextending throttle tab 54 of the throttle lever 28. The de-energizedstate, or neutral position, of the actuator means 18 may be overcome byappropriate manipulation of the accelerator mechanism by the driver. Ifthe actuator means 18 has not failed, manipulation of the acceleratormechanism by the driver will result in movement of the throttle lever 28and connected throttle valve 14 from the intermediate fluid flow,fail-safe position 26 toward the minimum fluid flow position 20 if theengine is idling, or toward the maximum fluid flow position 22 if fullengine power is desired. In the case of warm engine idle prior toactuator means failure, the throttle valve 14 would be moved into theminimum fluid flow position 20 with the first surface 32 of the throttlelever 28 engaging the first stop 34. This may be accomplished in a“drive-by wire” configuration by energizing the reversible electricmotor 42 to rotate the radially extending drive arm 44 and connecteddrive pin 46 in a clockwise direction to engage within the elongatedslot 48 of the throttle lever 28 to overcome the counterclockwiserotational urging of the helical fail-safe spring 68. The fail-safelever 50 is rotated clockwise in conjunction with the throttle lever 28through contact of the first surface 52 with the longitudinallyextending throttle tab 54 of the throttle lever 28 when moving in aclockwise direction from the intermediate fluid flow position 26. In thecase of increased engine power being required and prior to actuatormeans 18 failure, the throttle valve 28, as illustrated in FIG. 2, isdriven by the actuator means 18 in a counterclockwise direction. If thethrottle lever 28 is traveling in the counterclockwise direction fromthe minimum fluid flow position 20 described above, once the secondsurface 56 of the fail-safe lever 50 engages the fail-safe stop 58,further counterclockwise rotation of the fail-safe lever 50 isprevented. However, since the fail-safe lever 50 is supportedindependent of rotation of the shaft 30, further rotation of the shaft30 and connected throttle valve 14 is permitted. In a “drive-by wire”configuration, the reversible electric motor 42 may be energized in asuitable manner to drive the radially extending drive arm 44 andconnected drive pin 46 in the counterclockwise direction, as viewed inFIG. 2, and by engagement of the drive pin 46 within the elongated slot48 of the throttle lever 28 drive the throttle lever 28 in thecounterclockwise direction from the intermediate fluid flow position 26toward the maximum fluid flow position 22. If full engine power isrequired, the electric motor 42 may be energized sufficiently to drivethe throttle lever 28 so that the second surface 36 of the throttlelever 28 engages the second stop 38 holding the throttle valve 14 in themaximum fluid flow position 22. If less than full power is required, theelectric motor 42 may be energized sufficiently to hold the throttlevalve 14 in an angular position less than the maximum fluid flowposition 22. When the throttle valve 14 is in the minimum fluid flowposition 20, it typically is at an angle of approximately 7° withrespect to the plane of the throttle valve 14 being perpendicular to thelongitudinal axis of the fluid passage 16. During a normal warm engineidle at approximately 500 revolutions per minute, the throttle valve 14would be at a position between 7° and 9° from perpendicular to thelongitudinal axis of the fluid passage 16. The maximum fluid flowposition 22 would correspond to the plane of the throttle valve beingcontiguous with the longitudinal axis of the fluid passage 16. Theintermediate fluid flow position 26 would correspond to the throttlevalve 14 being at approximately 17° from perpendicular with respect tothe longitudinal axis of the fluid passage 16. It is believed that thisangular position of the throttle valve 14 is sufficient to allow theengine to develop enough power to move the vehicle in order to transportthe vehicle to a suitable repair center to fix the failed actuator means18.

In the event of actuator means 18 failure while the engine is idling andthe throttle lever 28 is disposed having the first surface 32 engagingthe first stop 34, the fail-safe spring means 60 overcomes the throttlespring means 40 to move the throttle lever 28 through contact with thefirst surface 52 of the fail-safe lever 50 and the longitudinallyextending throttle tab 54. The fail-safe spring means 60 urging thethrottle lever 28 to the intermediate fluid flow position 26. When thethrottle lever 28 reaches the intermediate fluid flow position 26, thesecond surface 56 of the fail-safe lever 50 reaches the fail-safe stop58 preventing further counterclockwise rotation, as illustrated in FIG.2, of the throttle lever 28 passed the fluid flow position 26. In thecase of actuator means 18 failure while the throttle lever 28 is in themaximum fluid flow position 22, the throttle spring means 40 will urgethe throttle lever 28 in the clockwise direction, as illustrated in FIG.2, until it reaches the intermediate fluid flow position 26. At theintermediate fluid flow position 26, the throttle spring means 40 lackssufficient force to overcome the counterclockwise urging of thefail-safe spring means 60 against the fail-safe lever 50 where the firstsurface 52 of the fail-safe /lever 50 prevents further clockwiserotation of the throttle lever 28 by engagement with longitudinallyextending throttle tab 54.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiments but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims, which scope is to be accorded the broadestinterpretation so as to encompass all such modifications and equivalentstructures as is permitted under the law.

1. A fail safe throttle positioning device for an engine inductionsystem comprising: a throttle body having a fluid passage passingtherethrough; a movable throttle valve for controlling at least idlespeed, said throttle valve mounted for movement with respect to saidthrottle body and disposed in said fluid passage for controlling fluidflow in response to movement of said throttle valve; actuator meansconnected to said throttle valve for operably moving said throttle valvebetween a minimum fluid flow position and a maximum fluid flow position;and fail safe means for urging said throttle valve toward anintermediate position between said minimum and maximum fluid flowpositions to prevent inoperability of said engine during actuator meansfailure.
 2. The device of claim 1 wherein said actuator means furthercomprises: a rotatable shaft supporting said throttle valve within saidfluid passage for rotational movement; a throttle lever connected tosaid shaft for rotation therewith, said throttle lever having a firstsurface engageable with a first stop defining a minimum fluid flowposition and a second surface engageable with a second stop defining amaximum fluid flow position; and throttle spring means for normallyurging said throttle lever toward said minimum fluid flow position. 3.The device of claim 2 wherein said fail safe means further comprises: afail safe lever mounted on said shaft for rotation independent of saidshaft, said fail safe lever having a first surface engageable with saidthrottle lever and a second surface engageable with a fail safe stop;and fail safe spring means for urging said fail safe lever toward saidfail safe stop such that said throttle lever is held in saidintermediate position until driven by said actuator means toward one ofsaid minimum and maximum fluid flow positions.
 4. The device of claim 3further comprising: a spacer sleeve mounted on said shaft external ofsaid throttle body; said fail safe spring means including a helicalspring extending longitudinally over said spacer sleeve and having afirst end connected to said throttle body and a second end connected tosaid fail safe lever; spring bushings disposed at longitudinal ends ofsaid fail safe spring and overlaying longitudinally at least a portionof said fail safe spring; and said throttle spring means including ahelical spring extending longitudinally over said spring bushings andhaving a first end connected to said throttle body and a second endconnected to said throttle lever.
 5. The device of claim 1 wherein saidactuator means further comprises: mechanically operated actuator meansconnected to said throttle lever and responsive to driver input.
 6. Thedevice of claim 1 wherein said actuator means further comprises:electrically operated actuator means connected to said throttle leverand responsive to driver input.
 7. A fail safe throttle positioningdevice for an engine induction system comprising: a throttle body havingan elongated fluid passage extending therethrough with a longitudinalaxis; an elongated shaft having a rotational axis generallyperpendicular to said longitudinal axis of said fluid passage; athrottle valve mounted on said shaft for rotational movement therewithand disposed within said fluid passage for controlling an amount offluid flow through said fluid passage in response to rotational movementof said shaft; a throttle lever connected to said shaft for rotationtherewith, said throttle lever having a first surface engageable with afirst stop defining a minimum fluid flow position and a second surfaceengageable with a second stop defining a maximum fluid flow position;throttle spring means for normally urging said throttle lever towardsaid minimum fluid flow position; actuator means connected to saidthrottle lever for operably moving said throttle lever against saidurging of said throttle spring means toward said maximum fluid flowposition; and fail safe means for urging said throttle lever toward anintermediate position between said minimum and maximum fluid flowpositions to prevent inoperability of said engine during failure of saidactuator means.
 8. The device of claim 7 wherein said fail safe meansfurther comprises: a fail safe lever rotatably mounted on said shaft,said fail safe lever having a first surface engageable with saidthrottle lever and a second surface engageable with a fail safe stop;and fail safe spring means for urging said fail safe lever toward saidfail safe stop such that said throttle lever is held in saidintermediate position until driven by said actuator means toward one ofsaid minimum and maximum fluid flow positions.
 9. The device of claim 8further comprising: a spacer sleeve mounted on said shaft external ofsaid throttle body; said fail safe spring means including a helicalspring extending longitudinally over said spacer sleeve and having afirst end connected to said throttle body and a second end connected tosaid fail safe lever; spring bushings disposed at longitudinal ends ofsaid fail safe spring and overlaying longitudinally at least a portionof said fail safe spring; and said throttle spring means including ahelical spring extending longitudinally over said spring bushings andhaving a first end connected to said throttle body and a second endconnected to said throttle lever.
 10. The device of claim 7 wherein saidactuator means further comprises: mechanically operated actuator meansconnected to said throttle lever and responsive to driver input.
 11. Thedevice of claim 7 wherein said actuator means further comprises:electrically operated actuator means connected to said throttle leverand responsive to driver input.
 12. A fail safe throttle positioningdevice for an engine induction system comprising: a throttle bodydefining a fluid passage; throttle valve means for controlling at leastidle speed, said throttle valve means mounted for movement within saidfluid passage to control fluid flow through said fluid passage bymovement of said throttle valve means; actuator means, connected to saidthrottle valve means, for moving said throttle valve means between aminimum fluid flow position and a maximum fluid flow position inresponse to input signals; fail safe means for urging said throttlevalve means toward an intermediate position between said minimum andmaximum fluid flow positions to prevent inoperability of said engineduring failure of said actuator means, said fail safe means includingcoaxial, counteracting, first and second helical spring means, saidfirst helical spring means for urging said throttle valve means towardsaid minimum fluid flow position and said second helical spring meansfor urging said throttle valve means toward an intermediate positionbetween said minimum and maximum fluid flow positions, said secondhelical spring means applying greater force to said throttle valve meansthan said first helical spring means.
 13. The device of claim 12 whereinsaid fail safe means further comprises: a fail safe lever connected tosaid throttle valve means, said fail safe lever having a first surfaceengageable with said throttle valve means and a second surfaceengageable with a fail safe stop; and said second helical spring meansfor urging said fail safe lever toward said fail safe stop such thatsaid throttle valve means is held in said intermediate position untildriven by said actuator means toward one of said minimum and maximumfluid flow positions.
 14. The device of claim 12 further comprising:said throttle valve means including a rotatable shaft; a spacer sleevemounted on said shaft external of said throttle body; said secondhelical spring means including a fail safe helical spring extendinglongitudinally over said spacer sleeve and having a first end connectedto said throttle body and a second end connected to said fail safemeans; spring bushings disposed at longitudinal ends of said fail safehelical spring and overlaying longitudinally at least a portion of saidfail safe helical spring; and said throttle valve means including athrottle return helical spring extending longitudinally over said springbushings and having a first end connected to said throttle body and asecond end connected to said throttle valve means.
 15. The device ofclaim 12 wherein said actuator means further comprises: mechanicallyoperated actuator means connected to said throttle lever and responsiveto driver input.
 16. The device of claim 12 wherein said actuator meansfurther comprises: electrically operated actuator means connected tosaid throttle lever and responsive to driver input.
 17. A fail safethrottle positioning device for an engine induction system comprising: athrottle body having a fluid passage extending through said throttlebody; a shaft extending across said fluid passage; a throttle valvemounted on said shaft for rotation and movement therewith and disposedwithin said fluid passage for controlling an amount of fluid flowthrough said fluid passage in response to rotational movement of saidshaft; a throttle lever connected to said shaft for rotation therewith,said throttle lever having a first surface engagable with a first stopdefining a minimum fluid flow position and a second surface engagablewith a second stop for defining a maximum fluid flow position; athrottle spring for urging said throttle lever toward said minimum fluidflow position; an actuator connected to said throttle lever for operablymoving said throttle lever against said urging of said throttle springtoward said maximum fluid flow position; and a fail safe spring forurging said throttle lever toward an intermediate position between saidminimum and maximum fluid flow positions to prevent inoperability ofsaid engine during failure of said actuator.
 18. The device of claim 17wherein said actuator further comprises an electrically operatedactuator connected to said throttle lever.
 19. The device of claim 17wherein said actuator further comprises a mechanically operated actuatorconnected to said throttle lever.
 20. The device of claim 17 whereinsaid fail safe spring and said throttle spring are nested substantiallywithin each other.
 21. The device of claim 17 wherein said fail safespring and said throttle spring are nested at least partially withineach other.
 22. The device of claim 17 wherein said fail safe spring andsaid throttle spring are axially juxtaposed to each other.
 23. Thedevice of claim 17 further comprising a fail safe lever rotatablymounted on said shaft to rotate independently of said shaft, whereinsaid fail safe lever is positioned between said fail safe spring andsaid throttle lever so that said fail safe lever urges said throttlelever toward said intermediate position.
 24. The device of claim 17further comprising: a fail safe lever rotatably mounted on said shaft,said fail safe lever having a first surface engageable with saidthrottle lever and a second surface engageable with a fail safe stop;and wherein said fail safe spring is operably engaged to said fail safelever and urges said fail safe lever toward said throttle lever suchthat said throttle lever is held in said intermediate position untildriven by said actuator toward one of said minimum and maximum fluidflow positions.
 25. The device of claim 24 wherein said throttle leverand said fail safe lever are axially juxtaposed.
 26. A fail safethrottle positioning device for an engine induction system comprising: athrottle body defining a fluid passage; a throttle valve mounted formovement within said fluid passage to control fluid flow through saidfluid passage by movement of said throttle valve; an actuator connectedto said throttle valve for moving said throttle valve between a minimumfluid flow position and a maximum fluid flow position in response toinput signals; a fail safe arrangement for urging said throttle valvetoward an intermediate position between said minimum and maximum fluidflow positions to prevent inoperability of said engine during failure ofsaid actuator, said fail safe arrangement including coaxial, first andsecond helical springs, said first helical spring for urging saidthrottle valve toward said minimum fluid flow position and said secondhelical spring for urging said throttle valve toward an intermediateposition between said minimum and maximum fluid flow positions, saidsecond helical spring applying greater force to said throttle valve thansaid first helical spring.
 27. The device of claim 26 wherein saidactuator further comprises an electrically operated actuator operablyconnected to said throttle lever.
 28. The device of claim 26 whereinsaid actuator further comprises a mechanically operated actuatorconnected to said throttle lever.
 29. The device of claim 26 whereinsaid fail safe arrangement further comprises a fail safe lever mountedon said shaft to rotate independently of said shaft, wherein said failsafe lever is positioned between said second spring and said throttlelever so that said fail safe lever urges said throttle lever toward saidintermediate position.
 30. The device of claim 26 further comprising: afail safe lever rotatably mounted on said shaft, said fail safe leverhaving a first surface engageable with a throttle lever operablyconnected to said throttle valve and said actuator and a second surfaceengageable with a fail safe stop; and wherein said second spring isoperably engaged to said fail safe lever and urges said fail safe levertoward said fail safe stop such that said throttle lever is held in saidintermediate position until driven by said actuator toward one of saidminimum and maximum fluid flow positions.
 31. The device of claim 30wherein said throttle lever and said fail safe lever are axiallyjuxtaposed.